(1) Field of the Invention
The invention relates to a method of wafer marking in the fabrication of integrated circuits, and more particularly, to a method of improved laser marking in the manufacture of integrated circuits.
(2) Description of the Prior Art
The fabrication of integrated circuits is accomplished by forming semiconductor devices on and within the surface of silicon wafers. Multiple chips or dice are formed on a wafer. In order to track the wafer and to identify the chips, laser identification marks are embedded into each wafer.
With the increasing number of metal layers and chemical mechanical polishing (CMP) processes, visibility and particle generation of the laser mark is becoming critically important. Typically, a laser beam is focused and pulsed in a pattern to create pits within the silicon to form these identification and tracking marks. The high energy pulses cause eruption of molten material from the wafer. The molten material is deposited adjacent to the laser marks forming ridges. These ridges formed in the conventional laser marking process cause micro-scratches to the surface of the wafer as they are dragged along the surface during the shallow trench isolation (STI) polishing process. These micro-scratches have been found to reduce yield. It is desired to find a process of laser marking that will enable good wafer identification marking visible on multi-layers without yield loss caused by micro-scratches.
U.S. Pat. No. 6,063,695 to Lin et al teaches cutting a laser mark, depositing a nonconformal layer, and then removing the ridges of material adjacent to the laser mark. The nonconformal layer protects the surface of the wafer during the removal process. U.S. Pat. No. 6,235,637 to Chen et al teaches forming a laser cut through a photoresist layer where the photoresist layer protects the wafer surface. U.S. Pat. No. 5,610,104 to Mitchell cuts a shallow laser mark, then oxidizes the substrate within the mark opening. The oxide is etched away to form the deep laser mark. U.S. Pat. No. 5,877,064 to Chang et al forms a laser mark on the non-patterned side of the wafer. U.S. Pat. No. 6,156,676 to Sato et al cuts a laser mark while flowing a gas to remove material so that the material is not deposited adjacent to the laser mark.
A principal object of the present invention is to provide an effective and very manufacturable method of forming a laser mark in the fabrication of integrated circuit devices.
Another object of the present invention is to provide an effective and very manufacturable method of forming a laser mark without damage to the wafer surface in the fabrication of integrated circuit devices.
In accordance with the objects of this invention a new method of forming a laser mark without damage to the wafer surface is achieved. A pad oxide layer is formed on a silicon wafer. A nitride layer is deposited overlying the pad oxide layer. A first trench is laser cut through the nitride layer and the pad oxide layer into the silicon wafer. The trench is etched to a second depth wherein the nitride layer is used as a hard mask and wherein the trench forms an identification mark.